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Equine January/February 2009 (Vol 4, No 1)

Therapeutics in Practice — Managing Foal Diarrhea

by Laurie A. Beard, DVM, MS, DACVIM

    Diarrhea is a common problem in foals, most of which experience one episode of diarrhea before they are 6 months of age. In most of these cases, the diarrhea is mild and medical treatment may not be necessary. In other cases, the diarrhea is severe with accompanying clinical signs of sepsis and septic shock, requiring aggressive medical treatment. The most common noninfectious causes of diarrhea in foals include foal heat and nutritional or dietary factors. The most common infectious causes of diarrhea in foals include rotavirus, Salmonella spp, Clostridium perfringens (types A and C are the most common), or Clostridium difficile. Less common causes of infectious diarrhea include coronavirus, Cryptosporidium parvum, other anaerobic bacteria, or Strongyloides westeri. Escherichia coli infection is a common cause of neonatal septicemia and is often listed as a cause of diarrhea in foals. However, the identification of enterotoxigenic E. coli is rare in foals, and E. coli is considered normal flora. The exact role of E. coli in equine neonatal diarrhea has not been determined. In addition to the pathogens already listed, infection with Lawsonia intracellularis (resulting in proliferative enteropathy) or parasites commonly causes diarrhea in older foals and weanlings. Rhodococcus equi infection can result in diarrhea in older foals but is uncommon. This article focuses on managing the most common causes of diarrhea in foals (from neonates to weanlings). Diagnostic testing for common pathogens that result in diarrhea in foals is discussed because diagnosis plays an important role in choosing the correct treatment and preventing outbreaks.

    Initial Management

    The initial management of foal diarrhea should be based on the patient's signalment, history, and physical examination. The foal's signalment provides important information for determining the etiology. For example, foal heat is the most common cause of diarrhea in foals 5 to 10 days of age. However, foals younger than 1 week have an increased risk for sepsis resulting from Salmonella, rotavirus, or clostridial infections. A history of diarrhea in other foals on the premises is highly suggestive of an infectious and contagious pathogen. The onset of diarrhea coincident with or following antimicrobial administration is suggestive of C. difficile infection. C. difficile is associated with antimicrobial use but can also be a primary pathogen in foals.1 A history of an inadequate deworming regimen in an older foal or weanling might suggest parasitism as a likely cause of diarrhea.

    A thorough physical examination is important for assessing the foal's condition and determining the appropriate treatment. For example, a bright, alert, afebrile 7-day-old foal that is nursing readily and has soft feces likely has foal heat diarrhea and requires minimal intervention. In contrast, a weak, depressed, recumbent foal with pipe-stream diarrhea requires significant intervention. A foal with diarrhea and clinical signs such as fever, depression, anorexia, and colic requires medical attention. To create a minimum database, blood should be collected to obtain a complete blood count, serum chemistry profile, and fibrinogen concentration. Additional diagnostic testing should include collection of feces for specific pathogen testing, assessment of passive transfer (the IgG concentration) in neonates, blood culture (aerobic and anaerobic), and arterial blood gas sampling.

    Characterization of the foal's diarrhea is imperative to diagnosis. Neonatal foals nursing from their dams have dog-like feces and usually have one or two bowel movements per day. Hemorrhagic diarrhea is strongly suggestive of clostridial enterocolitis. In contrast to diarrhea caused by other pathogens, clostridial diarrhea is usually not associated with failure of passive transfer.1,2 There is an increased risk of bacteremia in neonatal foals with Salmonella infections. Therefore, Salmonella spp should be high on the differential list for a neonate with diarrhea and septic arthritis. In many cases, the diarrhea associated with Salmonella, rotavirus, or clostridial infection is clinically indistinguishable, and all three possibilities should be considered. L. intracellularis infection should be high on the differential list for a 4- to 7-month-old foal with weight loss, edema, hypoproteinemia, and hypoalbuminemia. Abdominal ultrasonography (especially of foals with abdominal pain) can help assess bowel motility, detect distention of the small intestine, and measure bowel wall thickness. Abdominal ultrasonography of foals with clostridial enterocolitis may reveal gas and fluid-filled loops of large and small intestine. Segmental, marked thickening (6 to 12 mm; normal jejunum: 3 mm) of small intestine is often detected in foals infected with L. intracellularis. While not seen commonly, "dummy" foals with neonatal encephalopathy may develop necrotizing enterocolitis and segmental intestinal lesions with diarrhea.

    Diagnostic Testing for Common Pathogens

    Diagnostic testing is useful in managing foal diarrhea because some pathogens require specific treatment (Table 1). Diagnostic tests for Salmonella spp include fecal cultures (five serial fecal samples) and/or polymerase chain reaction (PCR) analysis of feces. Five serial fecal samples that test negative are considered the gold standard to rule out Salmonella infection. PCR is more sensitive for detecting Salmonella spp, requires less time than culture, and requires only one fecal sample; however, PCR techniques have limitations, including false-positive results and the inability to differentiate between live and inactivated organisms. Bacterial culture and sensitivity testing of Salmonella spp enables clinicians to choose the most appropriate antimicrobial treatment.

    Diagnostic tests for clostridial enterocolitis include fecal culture and toxin analysis. Toxin analysis is probably more important because there are nontoxigenic strains of C. difficile and C. perfringens, and it is often difficult to grow the anaerobic Clostridium spp in culture. Toxin analysis for C. difficile (toxins A and B) can be conducted using commercial immunoassays (ELISA) or PCR. Diagnosis of C. perfringens is more difficult. There is debate over exactly which toxin results in disease, and C. perfringens type A is also considered normal flora in foals and horses.3 C. perfringens type C is rarely found in the feces of normal horses and foals and results in more severe diarrhea than does type A.1-3 A commercial ELISA is available for detecting C. perfringens enterotoxin, but the importance of this toxin is unknown.1-3 Anaerobic culture of C. perfringens is recommended. The isolate should be typed by PCR analysis for toxin gene sequences.

    Diagnosis of rotavirus can be made by commercial assays (latex agglutination and ELISA) or electron microscopy. Electron microscopy can also identify less common viral pathogens, such as coronavirus. Further diagnostic tests for L. intracellularis include serology and PCR analysis of feces, but false-negative results have been reported.4 Parasitic infections that result in diarrhea in foals older than 3 months commonly include cyathostomes (small strongyles). Diagnosis of diarrhea due to small strongyles can be difficult because fecal egg counts can be low or negative as a result of prepatent or hypobiotic infection.

    Specific Treatments

    In neonatal foals or foals younger than 6 months with diarrhea accompanied by signs of sepsis (e.g., depression, lack of nursing, fever, hypothermia), broad-spectrum antimicrobials are indicated because of the risk of bacterial translocation across the compromised gastrointestinal (GI) barrier and possible bacteremia.1 Intravenous (IV) administration of antimicrobials is usually necessary in neonatal foals because of their small muscle mass and the long duration of antimicrobial administration. Commonly used antimicrobials include aminoglycosides (e.g. amikacin) and penicillin (Table 2). The aminoglycoside gentamicin is not recommended in foals, especially critically ill neonatal foals, because of potential nephrotoxicity. Third-generation cephalosporins such as ceftiofur sodium are an alternative. A high dose of ceftiofur sodium in neonatal foals is recommended by some clinicians5 (Table 2). Foals are at greater risk for bacteremia and sepsis due to Salmonella spp; therefore, antimicrobials effective against Salmonella spp (usually aminoglycosides or third-generation cephalosporins) are recommended.

    Metronidazole is recommended for treating clostridial colitis.1,2 There are reports of metronidazole-resistant C. difficile isolates from foals in certain geographic locations.6 Vancomycin is an antimicrobial commonly used to treat humans with C. difficile; however, because of concerns of development of resistance to vancomycin, particularly among multidrug-resistant bacteria, vancomycin should be used very carefully in veterinary patients.1,6 Other reported therapies for clostridial enterocolitis include the off-label use of C. perfringens C and D antitoxin (oral and IV administration),2 although its efficacy in foals is unknown. It is recommended that the antitoxin be given very slowly (and diluted in saline or lactated Ringer's solution). Pretreatment with diphenhydramine is recommended by some clinicians.2

    Antimicrobial choices recommended for treating L. intracellularis include oxytetracycline, doxycycline, macrolides (erythromycin, azithromycin, and clarithromycin, with or without rifampin), and chloramphenicol.7 I prefer oxytetracycline or doxycycline because of their low cost and reduced risk of diarrhea compared with that associated with macrolides (especially erythromycin) and because of human health concerns associated with chloramphenicol.7 A suspected small strongyle infection can be treated with a larvicide using fenbendazole for 5 days. Moxidectin (which may have larvicidal efficacy against small strongyles) is not recommended in foals younger than 4 months.

    Fluid Therapy

    In mild cases of diarrhea, normal hydration of foals may be maintained by nursing or by administration of oral fluids. Severely affected foals are often unable to maintain hydration without additional support, and neonatal foals are more likely than older foals to require IV fluid therapy. Assessment of hypovolemia is more difficult in neonatal foals than in adult horses, but clinical signs include dry, tacky oral mucous membranes, tachycardia, a prolonged capillary refill time (>2 seconds), sunken eyes, a poor pulse rate, and decreased urine production. Prolonged skin tenting can be difficult to observe in neonates because of poor skin turgor. Further assessment of hydration can be based on daily body weight (weight loss or failure to gain weight may indicate hypovolemia) and laboratory data (packed cell volume; total protein, albumin, and serum creatinine concentrations; and urine specific gravity). Reliance on serum total protein alone can be misleading because of the effects of passive transfer, loss of protein from the GI tract, or elevation of globulin and fibrinogen concentrations due to inflammation or infection. The serum creatinine concentration usually increases because of hypovolemia but can also be increased in renal failure or in newborn foals born to mares with placental insufficiency. If renal function is normal, the urine specific gravity can be useful. Neonatal foals usually have dilute urine (e.g., 1.001 to 1.002) in response to their diet of milk with a high water content. A urine specific gravity greater than 1.020 indicates that fluid losses are not being met. Hospitalization (or referral) is recommended for foals with diarrhea severe enough to warrant IV fluid therapy.

    A detailed discussion on the use of IV fluids and treatment of electrolyte abnormalities in foals is beyond the scope of this article, but there are several articles on this subject.1,8 The ideal crystalloid fluids for reestablishing normal hydration include lactated Ringer's solution, Plasma-Lyte 148 (Baxter International), or Normosol-R (Abbott Laboratories). To correct hypovolemia in neonatal foals, administration of IV fluid boluses (10 to 20 mL/kg [500 to 1000 mL for a 50-kg foal]) slowly (over 20 to 30 minutes) is recommended. Careful reevaluation of hydration status (clinical signs [e.g., mentation, pulse quality, distal limb temperature], laboratory data, and urine production) is recommended after administration of each bolus.

    Often, critically ill neonatal foals with severe diarrhea appear comatose and recumbent; however, after a few liters of IV fluids, the foals can sit in sternal recumbency or stand and become bright and alert. IV fluids are often continued to provide maintenance and replace ongoing losses. Maintenance fluid rates for neonates younger than 60 days are approximately 80 to 120 mL/kg/day (approximately 4 to 5 L for a 50-kg foal); these rates decrease to 60 mL/kg/day for foals older than 60 days. The ongoing fluid losses are difficult to determine in foals with diarrhea but can be estimated by the frequency, amount, and consistency of feces. If the ongoing losses are significant, fluids are often delivered at two to three times maintenance to maintain hydration. In many instances, fluids are given as a bolus because the foal is in the same stall with the mare. This should be attempted only in ambulatory foals that are not septic. If the foal is severely ill or recumbent, it should be separated from the mare to allow constant-rate infusion of fluids.

    Withholding or restriction of milk should be considered in foals with severe clostridial enterocolitis, colic, abdominal distention, and ileus.1 If milk is withheld or restricted, the administration of partial or total parenteral nutrition is necessary.1 Significant electrolyte and acid-base abnormalities are very common in foals with severe diarrhea; therefore, frequent laboratory testing (complete blood count, serum chemistry profile, arterial blood gas analysis) may be necessary to facilitate proper therapy and provide additional treatment, such as sodium bicarbonate therapy, when needed.

    Plasma and Colloids

    Plasma (1 to 2 L in a 50-kg foal) and synthetic colloids (e.g., hetastarch) are useful for increasing oncotic pressure and maintaining circulatory volume in foals with hypoproteinemia (<4 g/dL) and hypoalbuminemia (<2 g/dL). The foal's temperature, pulse, and respiration should be monitored closely during a plasma transfusion, and plasma should be delivered slowly to monitor for potential anaphylactic reactions. Plasma has additional benefits, including provision of antibodies (it is indicated in neonates with failure of passive transfer), clotting factors, antithrombin, and other proteins. Oral and IV plasma and hyperimmunized plasma (which is from horses vaccinated against clostridial toxins and Salmonella spp) may also help treat sepsis and endotoxemia.1

    Antiinflammatory and Antiendotoxic Medications

    The careful use of NSAIDs such as flunixin meglumine is indicated to provide analgesia and decrease inflammation, fever, and the effects of endotoxin; however, it is not recommended in foals younger than 1 month because of potential nephrotoxicity. NSAID use is not without risk, as it potentially reduces GI mucosal perfusion and decreases epithelial migration and healing.1 Therefore, it is important to avoid these drugs in volume-depleted foals or to use small doses (0.25 to 0.5 mg/kg q8-12h) as infrequently as possible.1 Polymyxin B, which is commonly given to adult horses to treat endotoxemia, is not used frequently in neonates because of concerns of nephrotoxicity (many septic foals present with azotemia).

    Intestinal Protectants and Absorbents

    Commonly used GI protectants include bismuth subsalicylate and kaolin/pectin products.1 Bismuth is used to coat the mucosa, and subsalicylate has some antiprostaglandin activity. Kaolin/pectin acts primarily as a mucosal binding agent. It is best to stagger administration of these medications with other oral drugs to avoid nonspecific binding and a reduction in bioavailability.1 Di-tri-octahedral (DTO) smectite, a commercially available natural hydrated clay silicate consisting of sheets of aluminum and magnesium, is effective for managing infectious colitis in humans and other animals. Two recent publications document that DTO smectite binds the exotoxins of C. difficile (toxins A and B) and C. perfringens (α-, β-, and β2-toxin and enterotoxin) to endotoxin in foals.9,10 The administration of DTO smectite should be withheld until at least 6 hours after ingestion of good-quality colostrum in foals younger than 24 hours because it may interfere with colostral absorption.10 Foals with rotavirus and clostridial enterocolitis can develop lactase deficiency secondary to the loss of the small intestinal brush border1; therefore, the use of lactase enzyme may be beneficial in these patients.

    The routine use of prophylactic gastric antiulcer medications is controversial in foals. However, in foals with diarrhea severe enough to necessitate treatment, the use of antiulcer medications may be indicated. Omeprazole, a very effective antiulcer drug, is widely used in foals; however, it is not labeled for use in foals younger than 4 weeks.1 The use of sucralfate could also be considered for treating gastric and other GI ulcers because it binds ulcers, increases local prostaglandin production, and increases local blood flow. Anecdotally, sucralfate also improves fecal consistency and may lead to constipation if given to a foal after diarrhea has resolved.

    Probiotics

    Probiotic administration is popular for treating colitis in horses. Until recently, the use of commercial probiotics in equine medicine was not supported by clinical studies. Saccharomyces boulardii, a nonpathogenic yeast, has been beneficial for preventing and treating colitis in humans. In a recent prospective, blinded, randomized study in adult horses with colitis, treatment with S. boulardii decreased the severity and duration of diarrhea.11 Cautious use of probiotics in foals (particularly those younger than 24 hours) has been suggested because of concerns of potential bacterial and fungal translocation.1 The use of S. boulardii has not been critically evaluated in foals, but some clinicians, including me, have used it in foals older than 1 week with diarrhea at a dose of 5 × 109 colony-forming units PO q12h.2

    Prevention and General Management

    Foals with diarrhea should be isolated from healthy mares and foals. It is important to practice good hygiene (e.g., foot baths) and wear protective clothing (e.g., gloves, disposable gowns or coveralls). Salmonella and clostridial organisms are also human pathogens; therefore, hand washing with antimicrobial soap or the use of an alcohol-based hand sanitizer is required for people handling foals with diarrhea.

    There are several commonly used disinfectants, each with different properties and antimicrobial spectrums. However, bleach or hypochlorite (recommended dilution of household bleach: 1:10) has a wide range of germicidal activity. Bleach is inactivated by organic matter and is not effective against rotavirus. Bleach is the most available sporicidal disinfectant, and its use should be considered (after cleaning to remove organic matter) in outbreaks of clostridial colitis. Phenolic disinfectants have broad germicidal activity against bacteria, viruses (including rotavirus), and fungi. Phenolic compounds are active in the presence of organic matter but are not sporicidal. Peroxygen compounds are newer disinfectants that are effective against a wide range of organisms and are not inactivated by organic matter. According to the manufacturer of Virkon S (DuPont), this peroxygen compound is also effective against bovine rotavirus and clostridial spores.

    Prevention of rotavirus outbreaks includes the use of a rotavirus vaccine during gestation (months 8, 9, and 10). Recommendations for preventing clostridial enterocolitis include the use of metronidazole (on newborn foals for 2 weeks), S. boulardii, and DTO smectite2; however, the prophylactic and widespread use of metronidazole in horses is not without concern.6 Treatment with metronidazole predisposes horses to colonization of metronidazole-resistant strains of C. difficile.6 Administration of C. perfringens types C and D antitoxin to foals younger than 6 hours on farms with a history of C. perfringens diarrhea has been recommended.2 Additional recommendations include vaccination of pregnant mares with C. perfringens C and D toxoid, but the safety and efficacy are unknown.2

    Conclusion

    Medical management of foals with diarrhea depends on the severity of the diarrhea and clinical signs. Foals with mild diarrhea and an otherwise normal physical examination can be managed with appropriate hygiene measures and careful monitoring of clinical signs. The use of bismuth subsalicylate, kaolin/pectin, sucralfate, DTO smectite, and S. boulardii may be beneficial in these cases. For foals with mild diarrhea that does not require extensive medical treatment, diagnostic testing for infectious (and contagious) pathogens may be helpful in preventing outbreaks of infectious diarrhea (such as on a large broodmare farm). For foals with diarrhea, clinical signs of sepsis, and hypovolemia, hospitalization, with frequent monitoring and aggressive fluid therapy, is often necessary.

    Downloadable PDF

    1. Magdesian KG. Neonatal foal diarrhea. Vet Clin North Am 2005;21:295-312.

    2. MacKay RJ. Equine neonatal clostridiosis: treatment and prevention. Compend Contin Educ Pract Vet 2001;23:280-284.

    3. Tillotson K, Traub-Dargatz JL, Dickinson CE, et al. Population-based study of fecal shedding of Clostridium perfringens in broodmares and foals. JAVMA 2002;220:342-348.

    4. McGurrin MK, Vengust M, Arroyo LG, Baird JD. An outbreak of Lawsonia intracellularis infection in a standardbred herd in Ontario. Can Vet J 2007;48:927-930.

    5. Magdesian KG. Neonatal pharmacology and therapeutics. In: Current Therapy in Equine Medicine. 5th ed. St. Louis: Saunders; 2003:1-5.

    6. Magdesian KG, Dujowich M, Madigan JE, et al. Molecular characterization of Clostridium difficile isolates from horses in an intensive care unit and association of disease severity with strain type. JAVMA 2006;228:751-755.

    7. Sampieri S, Hinchcliff KW, Toribio RE. Tetracycline therapy of Lawsonia intracellularis enteropathy in foals. Equine Vet J 2006;38:89-92.

    8. Palmer JE. Fluid therapy in the neonate: not your mother's fluid space. Vet Clin Equine 2004;20:63-75.

    9. Weese JS, Cote NM, deGannes RV. Evaluation of in vitro properties of di-tri-octahedral smectite on clostridial toxins. Equine Vet J 2003;35:638-641.

    10. Lawler JB, Hassel DM, Magnuson RJ, et al. Adsorptive effects of di-tri-octahedral smectite on Clostridium perfringens alpha, beta, and beta-2 exotoxins and equine colostral antibodies. Am J Vet Res 2008;69:233-239.

    11. Desrochers AM, Dolente BA, Roy MF, et al. Efficacy of Saccharomyces boulardii for treatment of horses with acute enterocolitis. JAVMA 2005;227:954-959.

    References »

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